Steel wire and steel cord for the reinforcing rubber article, and tire

ABSTRACT

This invention relates to steel wires and steel cords used as a reinforcement for rubber articles such as pneumatic tire, industrial belt and the like, particularly steel wires and steel cords having an excellent adhesion property to rubber, in which an amount of phosphorus included as an oxide in a surface layer region from a brass plated surface applied to a circumferential face of a wire up to a depth of 5 nm in a radial direction of the wire is controlled to not more than 1.5 atomic %, whereby an excellent adhesion property between steel cord and coating rubber can be provided even when an adhesion promoter conventionally added in a coating rubber composition for the steel cord is reduced or is not added.

TECHNICAL FIELD

[0001] This invention relates to a steel wire and a steel cord used as areinforcing member for rubber articles such as a pneumatic tire, anindustrial belt and the like, and more particularly to a steel wire anda steel cord having an excellent adhesion property to rubber.

BACKGROUND ART

[0002] In pneumatic tires as a typical example of the rubber article, itis attempted to mainly conduct the reinforcement with steel cords byapplying a rubberized steel cord made by twisting a plurality ofbrass-plated steel filaments or made of a single steel filament to abelt or a carcass. In order to utilize the steel cord as a reinforcingmember for the tire, it is required to surely adhere the steel cord to acoating rubber, and hence a peripheral face of a filament constitutingthe steel cord is subjected to a brass plating.

[0003] As to the brass plating, it is examined to adjust a ratio ofcopper to zinc in the brass, a plated thickness and the like forensuring the adhesion property to rubber, and hence a fixed knowledgetherefor is established.

[0004] By subjecting the filament constituting the steel cord to anadjusted brass plating based on the above knowledge is improved theadhesion property to rubber. Nevertheless, various conditions arerequired to rubber to be adhered. For example, it is required to ensurea sufficient adhesion force by an adhesion rate between cord and rubberor a complete bonding therebetween for curing and building a tire in acertain time. That is, a so-called initial adhesion property isrequired, so that it is necessary to add a sufficient ratio of Co saltor Ni salt as an adhesion promoter to rubber or to compound sulfur at ahigher ratio.

[0005] The thus added adhesion promoter including sulfur is effective topromote the adhesion reaction, but causes the oozing of the adhesionpromoter from the uncured rubber or so-called blooming of chemicals. Asa result, the operability in the plying of the uncured rubber sheet at,for example, a tire building step lowers and also the closing propertyor adhesion property between the uncured rubber sheet and rubber isobstructed and further a residue of the adhesion promoter in a curedrubber causes a cutting reaction of rubber molecule or a reversion,which result in the lowering of the tire durability.

[0006] From a viewpoint of preventing the occurrence of such problems,it is attempted to improve the adhesion property between a rubbercomposition containing no adhesion promoter and a cord by changing akind of the adhesion promoter, particularly a kind of an acid in Co saltor Ni salt, or by locating the adhesion promoter (cobalt metal salt) asa thin film between the coating rubber and the cord for decreasing theadhesion promoter in the coating rubber to be adhered with the steelcord. The latter technique is disclosed in, for example, JP-A-10-324753.

[0007] Incidentally, since the adhesion promoters, particularly adhesionpromoters such as cobalt metal salt and the like are expensive, thedecrease of the adhesion promoter in the coating rubber is effective tonot only improve the performances of the tire but also reduce thecompounding cost of rubber and is important from a viewpoint ofsource-saving.

[0008] However, the change in the kind of the adhesion promoter is onlythe application of a local optimization. Since the Co content is obligedto be basically the same, it is unavoidable to cause two-conflictingcondition that when the initial adhesion property is improved, theadhesion durability lowers or the blooming property lowers.

[0009] On the other hand, the method of locating the adhesion promoteras a thin film between the coating rubber and the cord as disclosed inJP-A-10-324753 is possible to certainly remove the compounding of Co inthe coating rubber. However, a ratio of Co diffused in the coatingrubber becomes inversely large before the adhesion reaction, so that itis required to arrange the thin film containing the adhesion promoter ata thickness of about several ten μm and hence it can not be said thatthe effect of decreasing Co is sufficient and a further improvement isdesired.

[0010] As to the adhesion between the coating rubber and the steel cordmade of brass-plated filament(s), there should be considered variousrequirements that not only the initial adhesion property is excellentbut also there is not caused a problem resulted from the deteriorationof rubber material including an adhesion boundary face between cord andrubber when the tire is placed in a deterioration environment during theuse, and further the operability at the tire production step is improvedand the compounding cost is controlled and the like.

[0011] As mentioned above, it is a first principal requirement that theinitial adhesion property is excellent as regards the adhesion propertybetween the steel cord made of brass-plated filament(s) and the rubbercoating it. For this end, it is examined to control the brass platingproperties on the surface of the filament, and there are reportedvarious examination results on a plating composition, particularly aplating composition on an outermost surface, a plated thickness, aninfluence of an oxidation degree of copper and zinc and the like. Also,there are proposals on the reduction of a phosphoric acid coating layerproduced in the drawing to exist on the outermost surface andcontributing to ensure the drawability.

[0012] However, the steel wire is required to take a work strengtheningby repeatedly subjecting a wire rod of, for example, about 5 mm to adrawing, so that the change in the plating influencing upon the drawingis naturally restricted. In fact, a surface brass-plated layer appliedto the wire and conducting an adhesion to rubber is largely differentfrom a matrix portion to be plated or the wire rod in the chemicalcomposition. For instance, the ratio of Cu and Zn contents is reverse,or the plated surface is frequently covered with a phosphoric acidcoating or zinc oxide to suppress the activity of the plated layeritself.

[0013] Furthermore, when the tire is placed in the deteriorationenvironment during the use, it is important to cause no problem resultedfrom the deterioration of the rubber material including the adhesionboundary between cord and rubber as previously mentioned. In thisconnection, the conventional adhesion promoter containing sulfur iseffective for promoting the adhesion reaction, but does not contributeto control the adhesion when the rubber-cord composite in the tire orthe like is exposed to water or oxygen (or active gas in air) under aheat environment and may promote the adhesion deterioration according tocircumstances. Therefore, when the tire and the like are used under athermally severe environment co-existing a relatively large amount ofwater and air, e.g. a high-temperature and high-humidity zone such assubtropical zones of Southeast Asia, it is important to improveso-called adhesion properties after the deterioration such as adhesionproperty in the resistance to moisture heat and the like in addition tothe improvement of the initial adhesion property. However, it isdifficult to simultaneously establish the initial adhesion property andthe adhesion properties after the deterioration.

[0014] In order to solve these problems on the adhesion property,JP-A-6-49783 proposes a technique focusing attention on the amount ofphosphoric acid at the surface of the wire constituting the steel cord.

[0015] However, this publication discloses that as the amount ofphosphoric acid remaining on the surface of the wire becomes large, theadhesion properties after the deterioration are excellent under ahigh-temperature and high-humidity environment but it is difficult toensure the initial adhesion property, while as the remaining phosphoricacid becomes small, the initial adhesion property is improved but theadhesion properties after the deterioration become insufficient. Forthis end, it is generally recognized that it is difficult tosimultaneously establish both the properties.

DISCLOSURE OF THE INVENTION

[0016] It is, therefore, a first object of the invention to establish away for giving an excellent adhesion property between a steel cord and acoating rubber in the brass plating applied to a wire constituting thesteel cord even if an adhesion promoter usually added to a coatingrubber composition for the steel cord is decreased or is not added.

[0017] In conjunction with the first object, a second object of theinvention is to establish a way of strongly ensuring an adhesionproperty to rubber in the brass plating applied to the wire constitutingthe steel cord by removing limitations on an outermost plated surface,which have hitherto been limited in a production process of the steelcord.

[0018] It is a third aspect of the invention to establish a way capableof improving adhesion properties after deterioration in addition to aninitial adhesion property as an adhesion property in the brass platingapplied to the wire constituting the steel cord.

[0019] The inventors have made various studies with respect to factorscontrolling an adhesion reaction between brass plating and rubber inorder to achieve the first object, and found that when a phosphoruscompound in a surface layer region of a brass plating is reduced as faras possible, an adhesion is completed in a very short time under aremarkably fast adhesion reaction inherent to the brass and that whenthe chemical composition of the brass plating is same, the adhesionproperty to rubber is substantially principally governed by thephosphorus compound in the plated surface layer. And also, it has beenconfirmed that the wire having the above reduced phosphorus compound inthe plated surface layer region can ensure the adhesion in a short timeeven if a cobalt salt as an adhesion promoter in rubber to be adhered isreduced or is not added.

[0020] Moreover, the control of an amount of phosphorus compound orphosphorus adhered to the wire surface to a given range with respect tothe adhesion property to rubber is disclosed, for example, inJP-B-7-8971, International Publication 97/23311 and the like. However,it is difficult to well maintain the adhesion property to rubber by suchan adjustment of the phosphorus adhered amount even when the adhesionpromoter is reduced or is not added.

[0021] Also, the phosphorus compound is a reaction product between thebrass and an extreme-pressure additive component among liquid lubricantsused in the drawing of the wire and has a function of reducing frictionbetween a die and the wire to control a temperature rise on the surfaceof the wire, so that it is an essential component in the drawing of thewire, and it is not too much to say that it is substantially impossibleto conduct the wire drawing without such a component. Therefore, thephosphorus compound is naturally included in the plated layer on thesurface of the wire after the drawing. Particularly, it is unavoidablethat the phosphorus compound is included in the plated layer of themass-produced wire.

[0022] Then, the inventors have made further examinations on the factorscontrolling the adhesion reaction between the brass plating and therubber in order to achieve the second object, and found that when thechemical composition of the brass plating is same, the adhesion propertyto rubber is substantially principally governed by the presence orabsence of a difference between copper content in the outermost surfaceof the plated layer and copper content in the plated layer itself.

[0023] In case of producing the wire by plating before the drawing, itis unavoidable that the chemical composition in the outermost surface ofthe plated layer in the resulting wire differs from the chemicalcomposition of the plated layer itself. Concretely, it has been foundthat the copper content in the outermost surface of the plated layer isalways lower than that of the plated layer.

[0024] Furthermore, the inventors have examined the adhesion propertyfrom various angles by strictly making up the plated surface layer withfree use of a precise instrumental analysis, which is not used up tonow, and a modifying way of a cord production process with respect tothe factor controlling the adhesion reaction between the brass platingand the cord in order to achieve the third object, and elucidated thatit is possible to simultaneously improve the initial adhesion propertyand the adhesion properties after the deterioration.

[0025] That is, it has newly been found that it is very important tocontrol a distribution of copper concentration from the surface of theplated layer in the wire toward an inside thereof as to the adhesionproperties after the deterioration. At the same time, it has been foundthat the distribution of copper concentration from the surface of theplated layer toward the inside thereof is varied by various factors suchas lubricant component and temperature in the drawing, pass schedule,die material, drawing rate and the like and hence it is necessary tostrictly control these factors in the production process.

[0026] The invention is based on the above knowledge and a gist andconstruction thereof are the followings 1-8.

[0027] 1. A steel wire for the reinforcement of rubber articles formedby subjecting a peripheral face of a wire to a brass plating,characterized in that an amount of phosphorus included as an oxide in asurface layer region from a surface of the brass plating up to a depthof 5 nm in a radial direction of the wire is controlled to not more than1.5 atomic %.

[0028] 2. A steel wire for the reinforcement of rubber articlesaccording to the item 1, wherein a ratio of copper to a total amount ofcopper and zinc in the surface layer region is 50-80 atomic %.

[0029] 3. A steel wire for the reinforcement of rubber articlesaccording to the item 2, wherein a copper content in the brass platedlayer is uniform in the radial direction of the wire.

[0030] 4. A steel wire for the reinforcement of rubber articlesaccording to the item 1, wherein when a distribution of a ratio ofatomicity of copper to total atomicity of copper, zinc, carbon andoxygen at a region from the surface of the brass plating up to a depthof 6 nm in the radial direction of the wire is approximated to quadraticfunction, a parameter in a variable term of second degree of thequadratic function is not more than −0.2 (atomic %/(nm)²).

[0031] 5. A steel wire for the reinforcement of rubber articlesaccording to any one of the items 1 to 4, wherein an average thicknessof the brass plated layer is 0.13-0.35 μm.

[0032] 6. A steel wire for the reinforcement of rubber articlesaccording to any one of the items 1 to 5, wherein a ratio of copper tosum of copper and zinc in the brass plated layer is 60-70% by weight,and a ratio of copper to sum of copper and zinc in the surface layerregion is 15-45 atomic %.

[0033] 7. A steel wire for the reinforcement of rubber articlesaccording to any one of the items 1 to 6, wherein a diameter of the wireis not more than 0.40 mm.

[0034] 8. A steel cord for the reinforcement of rubber articles,characterized by twisting a plurality of wires described in any one ofthe items 1 to 7.

[0035] 9. A tire comprising a carcass toroidally extending between apair of bead portions as a skeleton and a belt disposed outside thecarcass in a radial direction, characterized in that the steel wiredescribed in any one of the items 1 to 7 or the steel cord described inthe item 8 is used in either the carcass or the belt or both.

[0036] In general, the steel wire is produced by subjecting a wire rodhaving, for example, a diameter of about 5 mm to a drawing. In thisproduction process, a lubricant is naturally used. Particularly, thethinning of the wire is carried out at a final drawing step by usingdies of about 20 pass placed in a liquid lubricant. In this finaldrawing step, an extreme pressure is produced between the cord and thedie and also a temperature becomes very high, so that it is u usual touse a phosphoric acid based lubricant for ensuring the lubricity at anextreme pressure and a high temperature state.

[0037] This lubricant reacts with the surface of the wire in the drawingto form a lubrication film layer, i.e. a phosphorus compound layer andmitigates an input under a condition of extreme pressure and hightemperature to attain a mass production of the wire. In the productionprocess, therefore, it is unavoidable to incorporate phosphoric acid inthe plating of the wire.

[0038] The inventors have made various studies on the mechanism whereinphosphoric acid particularly existing at the plating side obstructs theadhesion to rubber as to the adhesion reaction of diffusing copper inthe brass plating containing phosphoric acid into rubber side to formCu_(x)S to thereby conduct adhesion. As a result, it has newly beenfound that the adhesion to rubber is not obstructed by phosphoric acidincorporated into a whole of the plating but is obstructed by aphosphorus compound existing in an extremely surface plating layercontacting with rubber, concretely a surface layer region from thesurface of the plating up to a depth of 5 nm in the radial direction ofthe wire. That is, the feature that the phosphorus compound does notremain in the surface layer region of the wire after the final drawingis essential in order to improve the adhesion property to rubber, whichis elucidated to be not solved by controlling an amount of phosphoricacid or phosphorus in the whole of the plated layer, for example, anamount of phosphoric acid or phosphorus as measured by dissolving in adiluted hydrochloric acid in the conventional technique.

[0039] Details arriving in the above knowledge will be described below.

[0040] At first, wires are prepared by variously changing a passschedule, a die material, a chemical composition of a lubricant,maturing conditions, a liquid temperature and so on at the drawing stepfor obtaining the aforementioned wire and then evaluated with respect tothe adhesion property to rubber, from which it is clear that theadhesion property to rubber differs in accordance with the wires. As aresult of examining conditions common to the wires having a goodadhesion property to rubber, the adhesion property to rubber is notcomprehended by a copper or phosphorus content in the plated layer asthe conventionally general indication as to the adhesion property torubber. For this end, there have made various studies on the factorexerting upon the adhesion property to rubber, and it has been foundthat an amount of phosphorus included as an oxide in an extremelysurface layer region of the plated layer, concretely a surface layerregion from the plated surface up to a depth of 5 nm in the radialdirection of the wire is interrelated to the adhesion property torubber.

[0041] In this case, the amount of phosphorus included as the oxide inthe surface layer region can be measured according to an X-rayphotoelectron spectroscopy. That is, atomicity of all elements andatomicity of phosphorus in the oxide are detected in a region of escapedepth of photoelectron measured according to the X-ray photoelectronspectroscopy, and the atomicity of phosphorus in the oxide isrepresented by an index on the basis that the atomicity of all elementsis 100 as an atomic % of phosphorus included in the oxide at the aboveregion. Moreover, the distinction between phosphorus as an oxide and theother phosphorus can be carried out based on a chemical shift of abonding energy of P=p photoelectron measured by an X-ray photoelectronspectrum of phosphorus atom. Also, the surface layer region up to thedepth of 5 nm can be recognized by a kinetic energy and an escape depthof an electron shown in a general literature on a solid photoelectronspectroscopy.

[0042] It is important to control the amount of phosphorus included asan oxide in the surface layer region to not more than 1.5 atomic %. Whenthe amount of phosphorus exceeds 1.5 atomic %, the adhesion rate torubber becomes slow and it is required to conduct a hard operation suchas strict regulation of rubber compounding for ensuring the desiredadhesion property to rubber or the like, and also an influence of watercontent in rubber becomes large and the adhesion property to rubber cannot be ensured in a winter season causing the lowering of the watercontent. By controlling the amount of phosphorus to not more than 1.5atomic %, it is possible to stably obtain the excellent adhesionproperty to rubber irrespectively of the water content in rubber.

[0043] As to the amount of copper in the plated layer, the coppercontent in the outermost plated surface participating the adhesionproperty to rubber is lower than that in the plated inside portion aspreviously mentioned. As a region having such a low copper content ismeasured, it is a region ranging from the plated surface up to a depthof 5-10 nm in the radial direction of the wire and being substantiallythe same region as mentioned on phosphorus. In such a region, it hasbeen found that the copper content has a concentration gradient ofgradually decreasing toward the surface.

[0044] The lowering of the copper content in the surface layer region ofthe plated layer is a factor degrading the adhesion property to rubberirrespectively of the same plating composition. In order to avoid theinfluence by the lowering of the copper content, it is important thatthe ratio of copper to sum of copper and zinc in the surface layerregion is not less than 50 atomic %. Preferably, the copper content inthe plated layer is made uniform in the radial direction of the wire.That is, it is recommended that copper has no concentration gradient.

[0045] On the other hand, when the ratio of copper to sum of copper andzinc in the surface layer region exceeds 80 atomic %, there is caused adisadvantage of lowering heat-resistant adhesion property andwater-proof adhesion property.

[0046] Further, the inventors have made the following examinations onthe adhesion property to rubber, particularly adhesion properties afterthe deterioration.

[0047] At first, the adhesion properties after the degradation, forexample, the deterioration of the adhesion property when the rubberarticle is used under a high-temperature and high-humidity environmentresults from the facts that Cu_(x)S participating the initial adhesionis decomposed by water and oxygen and that zinc in the plating reactswith water and oxygen to progress zinc-removal. In order to improve theadhesion properties after the deterioration, therefore, it is effectivethat the initial adhesion layer is uniform and dense and has a platingcomposition hardly progressing the zinc-removal. Concretely, it iseffective to control the concentration distribution of copper from thesurface of the plated layer in the depth direction thereof as mentionedlater.

[0048] That is, the concentration distribution of copper is controlledin a region from the plated surface up to a depth of 6 nm in the radialdirection of the wire. The reason why the range controlling theconcentration distribution of copper is the region from the platedsurface up to the depth of 6 nm is due to the fact that this region is aregion capable of diffusing copper in the plating dominating theuniformity and denseness of the adhesion layer, i.e. Cu required forforming Cu_(x)S.

[0049] In the region ranging up to the depth of 6 nm, it is importantthat when a distribution of a ratio of atomicity of copper to totalatomicity of copper, zinc, carbon and oxygen in the radial direction ofthe wire is approximated to quadratic function, a parameter in avariable term of second degree of the quadratic function is not morethan −0.2 (atomic %/(nm)²).

[0050] As an example of the distribution of the ratio of atomicity ofcopper to total atomicity of copper, zinc, carbon and oxygen in theradial direction of the wire is shown in FIG. 1, when a line segment Lconnecting measured values of copper concentration every depth of 1 nmin the region from the plated surface up to the depth of 6 nm in theradial direction of the wire is grasped as a quadratic function andrepresented by the following quadratic equation:

y=a(x−b)²−{(b ²−4ac)/4a},

[0051] the concentration distribution of copper is controlled so thatthe parameter a in the variable term of second degree of the linesegment L is not more than −0.2 (atomic %/(nm)²).

[0052] As shown by a comparative example in FIG. 1, it is common thatthe concentration distribution of copper in the conventional platedlayer linearly increases from the plated surface toward the insidethereof (parameter in the variable term of second degree is close tozero). On the contrary, in the plated layer having the controlledconcentration distribution of copper according to the invention, thereis a characteristic that since the parameter in the variable term ofsecond degree in the quadratic function is minus or a downward openslope, the copper concentration violently increases toward the inside ofthe plating. Moreover, the concentration distribution shown in FIG. 1shows results obtained by quantifying copper atoms every each depthwhile repeating an ion etching from the plated surface toward the insidethereof.

[0053] The reason why the adhesion properties after the deteriorationare improved by giving the above concentration distribution of copper tothe surface layer of the plating is guessed due to the fact that sincethe copper concentration inside the plating is higher that that in thesurface layer in the formation of Cu_(x)S, copper existing at rubberside produces an easily diffusing state. The adhesion properties afterthe deterioration are not always improved as the absolute value ofcopper becomes higher. Particularly, the feature that the parameter inthe variable term of second degree is not more than −0.2 (atomic%/(nm)²) has an effect of violently improving the adhesion property inthe resistance to moisture heat.

[0054] Also, it is preferable that the average thickness of the platedlayer is 0.13-0.35 μm. When the average thickness of the plated layer isless than 0.13 μm, a portion exposing an iron matrix increases toobstruct the initial adhesion property, while when it exceeds 0.35 μm,the adhesion reaction is excessively progressed by heat in the use ofthe rubber article and hence only a brittle adhesion is obtained.

[0055] Further, it is preferable that the ratio of copper to sum ofcopper and zinc in the brass plated layer is 60-70% by weight and theratio of copper to sum of copper and zinc in the surface layer region is15-45 atomic %. Firstly, when the ratio of copper to sum of copper andzinc in the plated layer as a whole is less than 60% by weight, thedrawability is degraded and the productivity is obstructed by wirebreaking and hence the mass production becomes difficult, and also it isdifficult to control the copper content in the surface layer region asmentioned later to not less than 15 atomic %. While, when it exceeds 70%by weight, the heat-resistant adhesion property and the waterproofadhesion property are degraded and the sufficient durability can not bemaintained under a tire exposed environment, and also it is difficult tocontrol the copper content in the surface layer region as mentionedlater to not more than 45 atomic %.

[0056] And also, when the ratio of copper to sum of copper and zinc inthe surface layer region is less than 15 atomic %, even if the amount ofphosphorus in the surface layer region is limited to not more than 1.5atomic %, the adhesion reaction to rubber is poor and it is difficult toensure the further excellent adhesion property to rubber. While, when itexceeds 45 atomic %, there is caused a disadvantage of loweringheat-resistant adhesion property and waterproof adhesion property.

[0057] The diameter of the wire is advantageous to be not more than 0.40mm. When it exceeds 0.40 mm, surface strain becomes large if the rubberarticle used is subjected to repetitive strain under a bendingdeformation and hence buckling is easily caused.

[0058] The above wire can form a steel cord suitable as a reinforcingmember of a rubber article, particularly a carcass or a belt of a tireby twisting a plurality of such wires. When the wire is applied to abelt of a passenger tire, particularly a passenger radial tire, theadhesion rate to rubber becomes fast, and it is possible to largelyshorten a curing time of the tire. On the other hand, when the wire isapplied to a carcass of a tire for truck and bus, particularly a radialtire for truck and bus, the adhesion rate to rubber becomes fast in thebead portion, and it is possible to improve the bead portion durabilityin addition to the shortening of the curing time.

[0059] In order to render the amount of phosphorus included in the oxideat the surface layer region, the phosphorus amount included in the oxideat the surface layer region can be controlled by conducting adjustmentsof pass schedule in the drawing, shape and angle of entrance or approachof the die, die material and composition of lubricant alone or in aproper combination thereof. Especially, it is very effective to conductthe drawing by using a die made of a material having an excellentself-lubricity and an excellent cutting property such as a sintereddiamond die in a final pass or in last several passes including thefinal pass among the dies of about 20 passes at a final drawing stepwhile using a lubricant containing an extreme-pressure additive in theusual manner at the final drawing step.

[0060] This way is effective even when the distribution of a ratio ofatomicity of copper to total atomicity of copper, zinc, carbon andoxygen in the region from the brass plated surface up to the depth of 6nm in the radial direction of the wire is approximated to quadraticfunction and a parameter in a variable term of second degree of thequadratic function is not more than −0.2 (atomic %/(nm)²).

[0061] On the other hand, it is desirable to adopt the following way inorder to provide the plated layer in which the ratio of copper to sum ofcopper and zinc in the surface layer region is not less than 50 atomic %and copper has no concentration gradient. That is, a mechanical abrasioncapable of removing the brass plated layer from the surface of the wireat an order of several nm with a cotton cloth impregnated with anorganic solvent or the like is adaptable. The production of industrialscale is made possible by properly incorporating the mechanical abrasioninto the production process of the wire.

[0062] In the heavy duty tires such as tires for truck and bus, tiresfor construction vehicles and the like, since the reinforcing degreewith the cords becomes higher, a wrapping wire is helically wound arounda bundle of plural twisted filaments to strengthen the bundle andmaintain the bundle at a given shape to thereby sufficiently develop arole as the cord. It is naturally required that this wrapping wiresurely adheres to rubber coating the steel cord, so that a peripheralface of the wrapping wire is subjected to a brass plating.

[0063] In the heavy duty tires used under an inflation of higherpressure, cords having a so-called multi-layer twisting structure or astrand twisting structure as shown, for example, in FIG. 2 are used as acord ruling the reinforcement. In this type of the cord, since awrapping wire 2 is helically wound on a peripheral face of a bundle ofmany filaments 1, even if a large bending input is applied to the tireduring the running under loading, the loosening of the filaments isprevented by the action of the wrapping wire 2 and hence the cord has anexcellent durability including a resistance to buckling fatigue.

[0064] Since the wrapping wire 2 is helically wound on the peripheralface of the filament bundle 3 as shown in FIG. 3, the wrapping wire 2 iseasily moved in an axial direction, for example, during the running ofthe tire under loading, and hence the wrapping wire 2 is relativelyshifted to a coating rubber 4 accompanied with the running for a longtime to cause a fear that an adhesion failure 5 is produced therebetweenas shown in FIG. 3(a). In an extreme case, the adhesion failure 5proceeds from FIG. 3(b) to FIG. 3(c) and finally the wrapping wire isbroken by rubbing with the coating rubber and further the filamentsthemselves in the cord are fretted and abraded with each other to bringabout the lowering of the cord tenacity.

[0065] This problem can be solved by omitting the wrapping wire.However, it is actually difficult to omit the wrapping wire in order tosatisfy various conditions required for the tire such as control of cordbuckling under the running under loading and so on when the tire is usedunder a heavy load.

[0066] Rather, when the adhesion property of the wrapping wire to rubberis improved, it is not necessary to discuss the omission of the wrappingwire and the lowering of the cord tenacity resulted from the adhesionfailure between the wrapping wire and rubber, and hence it is possibleto provide rubber articles such as tires and the like having anexcellent durability against the large bending input.

[0067] In order to improve the adhesion property between the wrappingwire and rubber while maintaining the excellent resistance to bucklingfatigue through the wrapping wire, therefore, it is advantageous tocontrol the amount of phosphorus included as an oxide in the surfacelayer region from the brass plated surface of the wrapping wire up tothe depth of 5 nm in the radial direction to not more than 1.5 atomic %likewise the case of the above cord body.

[0068] Even in the wrapping wire, it is effective that the ratio ofcopper to sum of copper and zinc in the surface layer region is 50-80atomic %, and that when the distribution of a ratio of number of copperatoms to total number of copper, zinc, carbon and oxygen atoms in theradial direction of the wire is approximated to quadratic function, theparameter in a variable term of second degree of the quadratic functionis not more than −0.2 (atomic %/(nm)²) as being expected for theimprovement of the adhesion properties after the deterioration.

BRIEF DESCRIPTION OF THE DRAWINGS

[0069]FIG. 1 is a graph showing a concentration distribution of copperin a depth direction of a plated layer;

[0070]FIG. 2 is a diagrammatically section view illustrating a cordstructure;

[0071]FIG. 3 is a schematic view illustrating an adhesion failurebetween a wrapping wire and a coating rubber and its progress; and

[0072]FIG. 4 is a graph showing a Cu concentration distribution in adepth direction of a plated layer.

BEST MODE FOR CARRYING OUT THE INVENTION EXAMPLE 1

[0073] With respect to steel cords produced according to specificationsshown in Tables 1-2 to 1-4, a test for adhesion property to rubber iscarried out according to a rubber adhesion test method defined inReference of JIS G3510 (1992). The results are shown in Tables 1-5 to1-8. A rubber compounding used in this adhesion test is shown in Table1-9. Moreover, Tables 1-5 and 1-6 show adhesion properties when a cobaltmetal salt is added in an amount usually used in a coating rubber, whileTables 1-7 and 1-8 show adhesion properties to coating rubber in case ofadding no cobalt salt. Further, the steel cords shown in Table 1-1 aremainly used as a belt cord in passenger car tires, tires for small-sizetruck and the like, while the steel cords shown in Table 1-2 are mainlyused as a belt cord and a carcass ply cord in tires for truck and bus.

[0074] Also, the quantitative determination of phosphorus in the surfacelayer region of the plated layer is conducted by an X-ray photoelectronspectroscopy, in which atomicities of C, Cu, Zn, O, P and N existing inthe plated surface layer region of the wire are measured at an analyzingarea of 20-30 μmφ not affected by curvature of the wire to determine aratio of atomicity of P when total atomicity of C, Cu, Zn, O, P and N is100. The atomicity of each of the atoms is determined by using countnumber of photoelectron of each of C:C_(1S), O:O_(1S), P:P_(2P),Cu:Cu_(2P3/2), Zn:Zn_(2P3/2) and N:N_(1S) and correcting with therespective sensitivity coefficient.

[0075] For instance, the detected atomicity of phosphorus [P] can bedetermined by the following equation:

[P]=F_(P) (sensitivity coefficient of P_(2P))×(count of P_(2P)photoelectron per constant time)

[0076] Also, the detected atomicity with respect to the other atoms isdetermined in the same manner as mentioned above, from which results arelative atomic % of phosphorus can be determined by the followingequation:

P%={[P]/([Cu]+[Zn]+[C]+[O]+[N]+[P])}×100

[0077] Moreover, when the surface of the wire before the analysis iscovered with an oil or the like or contaminated with an organicsubstance, it is washed with a proper solvent and further subjected to aslight argon ion etching to an extent not modifying the surface, ifnecessary. TABLE 1-1 Comparative Invention Invention ComparativeInvention Invention Example 1-1 Example 1-1 Example 1-2 Example 1-2Example 1-3 Example 1-4 Cord construction 1 × 3 × 0.30 1 × 3 × 0.30 1 ×3 × 0.30 1 × 5 × 0.225 1 × 5 × 0.225 1 × 5 × 0.225 (mm) (mm) (mm) (mm)(mm) (mm) Extreme pressure additive in drawing use use use use use useTensile strength of wire (N/mm²) 3400 3400 3400 3300 3300 3300 PlatingCu/Zn composition 63/37 63/37 63/37 63/37 63/37 63/37 properties Platingthickness (μm) 0.25 0.25 0.25 0.21 0.21 0.21 Surface layer region (*1)28 31 35 30 32 35 Cu content (*2) (atomic %) P content in plated layer(*3) 1.17 1.18 1.05 0.91 0.91 0.82 (mg/m²) Surface layer region (*1)2.50 1.50 1.00 1.70 1.20 0.95 P content (atomic %) Rubber CompoundingNo. A A A A A A composition Amount of cobalt salt (*4) 2 parts by 2parts by 2 parts by 2 parts by 2 parts by 2 parts by used weight weightweight weight weight weight

[0078] TABLE 1-2 Comparative Invention Invention Comparative InventionInvention Example 1-3 Example 1-5 Example 1-6 Example 1-4 Example 1-7Example 1-8 Cord construction (1 + 6) × 0.34 (1 + 6) × 0.34 (1 + 6) ×0.34 (3 + 8) × 0.21 (3 + 8) × 0.21 (3 + 8) × 0.21 (mm) (mm) (mm) (mm)(mm) (mm) Extreme pressure additive in drawing use use use use use useTensile strength of wire (N/mm²) 3200 3200 3200 3700 3700 3700 PlatingCu/Zn composition 63/37 63/37 63/37 63/37 63/37 63/37 properties Platingthickness (μm) 0.32 0.32 0.32 0.21 0.21 0.21 Surface layer region (*1)28 30 33 30 32 36 Cu content (*2) (atomic %) P content in plated layer(*3) 1.12 1.07 1.14 0.66 0.65 0.64 (mg/m²) Surface layer region (*1)2.00 1.40 1.00 1.80 1.30 0.94 P content (atomic %) Rubber CompoundingNo. A A A A A A composition Amount of cobalt salt (*4) 2 parts by 2parts by 2 parts by 2 parts by 2 parts by 2 parts by used weight weightweight weight weight weight

[0079] TABLE 1-3 Comparative Invention Invention Invention Example 1-5Example 1-9 Example 1-10 Example 1-11 Cord construction 1 × 5 × 0.225 1× 5 × 0.225 1 × 5 × 0.225 1 × 5 × 0.225 (mm) (mm) (mm) (mm) Extremepressure additive in use use use use drawing Tensile strength of wire(N/mm²) 3300 3300 3300 3300 Plating Cu/Zn composition 63/37 63/37 63/3763/37 properties Plating thickness 0.25 0.21 0.21 0.21 (μm) Surfacelayer 30 32 35 38 region (*1) Cu content (*2) (atomic %) P content inplated 0.91 0.91 0.82 0.80 layer (*3) (mg/m²) Surface layer 1.70 1.200.95 0.80 region (*1) P content (atomic %) Rubber Compounding No. B B BB composition Amount of cobalt 0 part by 0 part by 0 part by 0 part byused salt (*4) weight weight weight weight

[0080] TABLE 1-4 Comparative Invention Invention Invention Example 1-6Example 1-12 Example 1-13 Example 1-14 Cord construction (3 + 8) × 0.21(3 + 8) × 0.21 (3 + 8) × 0.21 (3 + 8) × 0.21 (mm) (mm) (mm) (mm) Extremepressure additive in use use use use drawing Tensile strength of wire(N/mm²) 3700 3700 3700 3700 Plating Cu/Zn composition 63/37 63/37 63/3763/37 properties Plating thickness 0.21 0.21 0.21 0.21 (μm) Surfacelayer 30 32 36 38 region (*1) Cu content (*2) (atomic %) P content inplated 0.66 0.65 0.64 0.61 layer (*3) (mg/m²) Surface layer 1.80 1.310.94 0.75 region (*1) P content (atomic %) Rubber Compounding No. B B BB composition Amount of cobalt 0 part by 0 part by 0 part by 0 part byused salt (*4) weight weight weight weight

[0081] TABLE 1-5 Comparative Invention Invention Comparative InventionInvention Example Example Example Example Example Example 1-1 1-1 1-21-2 1-3 1-4 Adhesion Rubber adhesion 0 60 100 40 100 100 propertiesratio after the curing of 160° C. × 5 minutes (%) Rubber adhesion 20 100100 80 100 100 ratio after the curing of 160° C. × 9 minutes (%) Rubberadhesion 85 100 100 95 100 100 ratio after the curing of 160° C. × 13minutes (%) Rubber adhesion 100 100 100 100 100 100 ratio after thecuring of 160° C. × 18 minutes (%)

[0082] TABLE 1-6 Comparative Invention Invention Comparative InventionInvention Example Example Example Example Example Example 1-3 1-5 1-61-4 1-7 1-8 Adhesion Rubber adhesion 0 75 100 0 80 100 properties ratioafter the curing of 145° C. × 7.5 minutes (%) Rubber adhesion 0 90 10015 90 100 ratio after the curing of 145° C. × 10 minutes (%) Rubberadhesion 15 95 100 45 95 100 ratio after the curing of 145° C. × 15minutes (%) Rubber adhesion 60 97 100 85 95 100 ratio after the curingof 145° C. × 20 minutes (%) Rubber adhesion 60 100 100 98 100 100 ratioafter the curing of 145° C. × 30 minutes (%)

[0083] TABLE 1-7 Comparative Invention Invention Invention Example 1-5Example 1-9 Example 1-10 Example 1-11 Adhesion Rubber adhesion 0 50 6090 properties ratio after the curing of 160° C. × 7 minutes (%) Rubberadhesion 25 80 85 98 ratio after the curing of 160° C. × 9 minutes (%)Rubber adhesion 45 90 95 100 ratio after the curing of 160° C. × 11minutes (%) Rubber adhesion 60 97 98 100 ratio after the curing of 160°C. × 13 minutes (%) Rubber adhesion 70 100 100 100 ratio after thecuring of 160° C. × 15 minutes (%)

[0084] TABLE 1-8 Comparative Invention Invention Invention Example 1-6Example 1-12 Example 1-13 Example 1-14 Adhesion Rubber adhesion 5 20 8095 properties ratio after the curing of 160° C. × 5 minutes (%) Rubberadhesion 20 50 90 100 ratio after the curing of 160° C. × 9 minutes (%)Rubber adhesion 60 90 95 100 ratio after the curing of 160° C. × 13minutes (%) Rubber adhesion 70 98 99 100 ratio after the curing of 160°C. × 18 minutes (%) Rubber adhesion 70 100 100 100 ratio after thecuring of 160° C. × 15 minutes (%)

[0085] TABLE 1-9 Compounding No. A B NR 100 100 HAF 50 50 ZnO 5 5 Cosalt of naphtenic acid (10%) 2 0 Sulfur 5 5 Vulcanization accelerator DZ0.5 0.5

[0086] Comparative Example 1-1 in Table 1-5 shows a result of anadhesion peeling test between a steel cord of 1×3×0.30 (mm) using theconventional wire and a coating rubber usually used, while ComparativeExample 1-2 shows a result of an adhesion peeling test between a steelcord of 1×5×0.225 (mm) using the conventional wire and a coating rubberusually used.

[0087] On the other hand, Invention Example 1-1 is an example wherein Pin the plated surface layer region of the final wire is reduced to 1.50atomic % by properly changing a drawing lubrication condition and usinga sintered diamond die as a die in a suitable latter stage in the finaldrawing under the same heat treatment as in Comparative Example 1-1.Similarly, Invention Example 1-2 is an example wherein P in the platedsurface layer region of the final wire is reduced to 1.00 atomic %.

[0088] A rubber adhesion ratio of 100% is not ensured unless a curingtime at 160° is 18 minutes in Comparative Example 1-1 and about 13minutes in Comparative Example 1-2. On the contrary, the rubber adhesionratio of 100% is attained by curing at 160° C. for 9 minutes inInvention Example 1-1, while the rubber adhesion ratio of 100% isensured even for about 5 minutes, which does not completely cure therubber, in Invention Example 1-2. Similarly, the rubber adhesion ratioof 100% is obtained at 160° C. for 5 minutes in Invention Examples 1-3and 1-4 because it is possible to more easily reduce P in the surfacelayer region though it is guessed that the diameter of the wire is thinand the tensile strength is low. When the amount of the adhesionpromoter usually added is used in the rubber composition, if P amount inthe surface layer region of the plated wire is not more than 1.5 atomic%, the adhesion rate can significantly be improved and it is possible toextensively improve the productivity such as shortening of curing timein the tire or the like.

[0089] Then, Table 1-2 shows a case that a cord of a layer constructionis mainly used in a large-size tire, and Invention Examples 1-5 and 1-6are cases of cords particularly suitable for the belt that the diameteris as thick as 0.34 mm and the tensile strength is higher. When theInvention Examples 1-5 and 1-6 are compared with Comparative Example 1-3conducting the same production process up to the drawing, the InventionExamples 1-5 and 1-6 attain the significant improvement of the adhesionrate as shown in Table 1-6 because the reduction of P amount in theplated surface layer region is successful.

[0090] Also, Invention Examples 1-7 and 1-8 are cases of cords suitablefor carcass ply that the diameter is as thin as 0.21 mm and the tensilestrength is a highest class. When the Invention Examples 1-7 and 1-8 arecompared with Comparative Example 1-4 conducting the same productionprocess up to the drawing, the Invention Examples 1-7 and 1-8 attain thesignificant improvement of the adhesion rate because the reduction of Pamount in the plated surface layer region is successful. That is, as theP amount in the plated surface layer region is reduced to not more thana half of a usual level (not more than 1.00 atomic %), the rubberadhesion ratio of 100% can be ensured at 145° C. in about 7.5 minutes.In case of the large-size tire, it is general to conduct the curing at alower temperature as compared with the small-size tire in view of thetire durability, so that the curing time becomes naturally long and isfrequently restricted to the adhesion rate of rubber. Therefore, thesignificant improvement of the adhesion rate is immediately madepossible to bring about the increase of the production number of tires.Furthermore, the shortening of the curing time is related to the controlof degrading the properties of the over-cured material and cancontribute to improve the tire performances.

[0091] Comparative Example 1-5 shown in Table 1-7 shows a result of anadhesion peeling test between a steel cord of 1×5×0.225 (mm) using theconventional filaments and rubber obtained by removing the adhesionpromoter from the usually used coating rubber. On the contrary,Invention Examples 1-9, 1-10 and 1-11 are cases of reducing P amount inthe surface layer region of the final plated wire to 1.2-0.8 atomic % byproperly changing a drawing lubrication condition and using a sintereddiamond die as a die in a suitable latter stage in the final drawingunder the same heat treatment as in Comparative Example 1-5. InComparative Example 1-5, the rubber adhesion ratio of 100% can not beensured even in the curing of 160° C. for 15 minutes. On the other hand,the adhesion property to rubber can be improved to a level exceeding theadhesion property to rubber containing the adhesion promoter shown inComparative Example 1-2 by reducing the P amount in the plated surfacelayer region in the order of Invention Examples 1-9, 1-10 and 1-11.

[0092] Comparative Example 1-6 shown in Table 1-8 shows a result of anadhesion peeling test between a steel cord of (3+8)×0.21 (mm) using theconventional filaments and rubber obtained by removing the adhesionpromoter from the usually used coating rubber. On the contrary,Invention Examples 1-12, 1-13 and 1-14 are cases of reducing P amount inthe surface layer region of the final plated wire to 1.31-0.75 atomic %by properly changing a drawing lubrication condition and using asintered diamond die as a die in a suitable latter stage in the finaldrawing under the same heat treatment as in Comparative Example 1-6. InComparative Example 1-6, the rubber adhesion ratio of 100% can not beensured even in the curing of 145° C. for 30 minutes and also theadhesion can not be completed. On the other hand, the adhesion propertyto rubber can be improved to a level exceeding the adhesion property torubber containing the adhesion promoter shown in Comparative Example 1-4by reducing the P amount in the plated surface layer region in the orderof Invention Examples 1-12, 1-13 and 1-14. Especially, in the InventionExample 1-14, the rubber adhesion ratio of approximately 100% withrespect to rubber containing no cobalt can be ensured even in the curingof 145° C. for 10 minutes, so that it is possible to shorten the curingtime but also remove various harmful effects of the adhesion promoter.

[0093] From the comparisons in the above Tables, it is clear that thewires according to the invention belong to category quite different fromtechniques disclosed in JP-B-7-8971 and International Publication97/23311 as a prior art in not only the content but also the effects.

EXAMPLE 2

[0094] With respect to steel cords produced according to specificationsshown in Tables 2-1 and 2-2, a test for adhesion property to rubber iscarried out at room temperature (RT) and a lower temperature of −60° C.(LT) according to a rubber adhesion test method defined in Reference ofJIS G3510 (1992), respectively. The results are shown in Tables 2-3 and2-4. A rubber compounding used in this adhesion test is shown in theaforementioned Table 1-9. Moreover, the steel cords shown in Table 2-1are mainly used as a belt cord in passenger car tires, tires forsmall-size truck and the like, while the steel cords shown in Table 2-2are mainly used as a belt cord and a carcass ply cord in tires for truckand bus.

[0095] And also, the distribution of copper concentration (atomic %) inthe plated layer in the radial direction of the wire with respect someexamples shown in Tables 2-1 and 2-2 is shown in FIG. 4, while thephosphorus concentration (mass %) on the plated surface in theseexamples is shown in Table 2-5.

[0096] In this case, the amount of phosphorus in the surface layerregion of the plated layer is quantified in the same manner as inExample 1. Also, the concentration of copper is possible to bequantified in the same manner as mentioned above.

[0097] Further, it is possible to measure the distribution of copperconcentration from the plated surface toward the inside thereof bycombining with ion etching, in which an actual depth can be convertedfrom an etching rate to a brass foil having a known thickness.

[0098] Moreover, when the surface of the wire before the analysis iscovered with an oil or the like or contaminated with an organicsubstance, it is washed with a proper solvent and further subjected to aslight argon ion etching to an extent not modifying the surface, ifnecessary. TABLE 2-1 Comparative Invention Invention ComparativeInvention Example 2-1 Example 2-1 Example 2-2 Example 2-2 Example 2-3Cord construction 1 × 3 × 0.30 1 × 3 × 0.30 1 × 3 × 0.30 1 × 3 × 0.30 1× 3 × 0.30 (mm) (mm) (mm) (mm) (mm) Extreme pressure additive in drawinguse use use use use Phosphorus reducing treatment none after after ondrawing on and after of plated surface drawing drawing drawing Tensilestrength of wire (N/mm²) 3400 3400 3400 3400 3400 Plating Cu/Zncomposition 63/37 63/37 63/37 63/37 63/37 properties Plating thickness(μm) 0.25 0.25 0.25 0.25 0.25 Surface layer region (*1) 2.50 1.50 0.901.00 0.1 P content (atomic %) P content in plated layer (*3) 1.15 1.151.03 1.00 1.02 (mg/m²) Surface layer region (*1) 23 51 53 25 62.5 Cucontent (atomic %) Cu content from plated 45 61 62 45 62.5 surface todepth of 4 mm (atomic %) Cu content from plated 57 62.5 62.5 55 62.5surface to depth of 6 mm (atomic %) Rubber Compounding No. A A A A Acomposition Amount of cobalt salt (*4) 2 parts by 2 parts by 2 parts by2 parts by 2 parts by used weight weight weight weight weight

[0099] TABLE 2-2 Comparative Invention Comparative Invention Example 2-3Example 2-4 Example 2-4 Example 2-5 Cord construction (3 + 8) × 0.21(3 + 8) × 0.21 (3 + 8) × 0.21 (3 + 8) × 0.21 (mm) (mm) (mm) (mm) Extremepressure additive in drawing use use use use Phosphorus reducingtreatment none after on drawing on and after of plated surface drawingdrawing Tensile strength of wire (N/mm²) 3700 3700 3700 3700 PlatingCu/Zn composition 63/37 63/37 63/37 63/37 properties Plating thickness(μm) 0.21 0.21 0.21 0.21 Surface layer region (*1) 1.80 1.31 0.94 0.1 Pcontent (atomic %) P content in plated layer (*3) 1.12 1.10 1.07 1.05(mg/m²) Surface layer region (*1) 30 60 32 62.5 Cu content (atomic %) Cucontent (atomic %) at 49 62.5 50 62.5 a depth point of 4 mm from platessurface Cu content (atomic %) at 62.5 62.5 62.5 62.5 a depth point of 6mm from plates surface Rubber Compounding No. B B B B composition Amountof cobalt salt (*4) 0 parts by 0 parts by 0 parts by 0 parts by usedweight weight weight weight

[0100] TABLE 2-3 Comparative Invention Invention Comparative InventionExample Example Example Example Example 2-1 2-1 2-2 2-2 2-3 AdhesionRubber adhesion RT 0 75 100 100 100 properties ration after the LT 0 4080 70 90 curing of 160° C. × 5 minutes (%) Rubber adhesion RT 20 100 100100 100 ration after the LT 0 60 90 95 100 curing of 160° C. × 9 minutes(%) Rubber adhesion RT 85 100 100 100 100 ration after the LT 20 90 10098 100 curing of 160° C. × 13 minutes (%) Rubber adhesion RT 100 100 100100 100 ration after the LT 50 95 100 100 100 curing of 160° C. × 18minutes (%)

[0101] TABLE 2-4 Comparative Invention Comparative Invention ExampleExample Example Example 2-3 2-4 2-4 2-5 Adhesion Rubber adhesion rationRT 5 80 80 100 properties after the curing of LT 0 25 25 75 145° C. × 10minutes (%) Rubber adhesion ration RT 20 95 90 100 after the curing ofLT 0 50 55 98 145° C. × 15 minutes (%) Rubber adhesion ration RT 60 9595 100 after the curing of LT 10 70 75 100 145° C. × 20 minutes (%)Rubber adhesion ration RT 70 100 99 100 after the curing of LT 20 95 95100 145° C. × 25 minutes (%) Rubber adhesion ration RT 70 100 100 100after the curing of LT 20 100 100 100 145° C. × 30 minutes (%)

[0102] TABLE 2-5 Surface layer region P content Comparative Example 1:usual drawn product 2.5 atomic % Invention Example 1: usual drawing +1.5 atomic % one polishing treatment Invention Example 2: usualdrawing + 0.9 atomic % two polishing treatments Comparative Example 2:improved drawing 1.0 atomic % Invention Example 3: improved drawing +0.1 atomic % one polishing treatment

EXAMPLE 3

[0103] With respect to steel cords produced according to specificationsshown in Tables 3-1 and 3-2, a test for adhesion property to rubber iscarried out according to a rubber adhesion test method defined inReference of JIS G3510 (1992). Also, adhesion properties after thedeterioration are evaluated by the above test for adhesion property torubber after it is left to stand in an atmosphere of humidity: 100% andtemperature: 75° C. for 2-6 days. The results are shown in Tables 3-3and 3-4. A rubber compounding used in this adhesion test is shown in theaforementioned Table 1-9. Moreover, Table 3-3 shows adhesionperformances in case of adding an amount of cobalt metal salt usuallyused in the coating rubber, and Table 3-4 shows adhesion performances tothe coating rubber in case of adding no cobalt salt. Further, the steelcords shown in Tables 3-1 and 3-2 are mainly used as a belt cord inpassenger car tires, tires for small-size truck and the like, while areeasily affected by an active component from exterior in use.

[0104] And also, the amount of phosphorus in the surface layer region ofthe plated layer is quantified in the same manner as in Example 1.Moreover, when the surface of the wire before the analysis is coveredwith an oil or the like or contaminated with an organic substance, it iswashed with a proper solvent and further subjected to a slight argon ionetching to an extent not modifying the surface, if necessary. TABLE 3-1Comparative Comparative Invention Invention Invention Invention Example3-1 Example 3-2 Example 3-1 Example 3-2 Example 3-3 Example 3-4 Cordconstruction 1 × 3 × 0.30 1 × 3 × 0.30 1 × 3 × 0.30 1 × 3 × 0.30 1 × 3 ×0.30 1 × 3 × 0.30 (mm) (mm) (mm) (mm) (mm) (mm) Extreme pressureadditive in drawing use use use use use use Tensile strength of wire(N/mm²) 3400 3400 3400 3400 3400 3400 Plating Cu/Zn composition 63/3763/37 63/37 63/37 63/37 63/37 properties Plating thickness (μm) 0.250.25 0.25 0.25 0.25 0.25 Surface layer region (*1) 30 30 31 31 31 31 Cucontent (*2) Second parameter of copper −0.2 −0.016 −0.25 −0.3 −0.5−0.78 concentration distribution at a depth region of 6 mm P content inplated layer (*3) 1.98 1.70 1.80 2.01 1.80 1.50 (mg/m²) Surface layerregion (*1) 2.50 1.50 1.00 1.10 1.00 0.90 P content (atomic %) RubberCompounding No. A A A A A A composition Amount of cobalt salt (*4) 2parts by 2 parts by 2 parts by 2 parts by 2 parts by 2 parts by usedweight weight weight weight weight weight

[0105] TABLE 3-2 Comparative Comparative Invention Invention InventionInvention Example 3-3 Example 3-4 Example 3-5 Example 3-6 Example 3-7Example 3-8 Cord construction 1 × 3 × 0.30 1 × 3 × 0.30 1 × 3 × 0.30 1 ×3 × 0.30 1 × 3 × 0.30 1 × 3 × 0.30 (mm) (mm) (mm) (mm) (mm) (mm) Extremepressure additive in drawing use use use use use use Tensile strength ofwire (N/mm²) 3400 3400 3400 3400 3400 3400 Plating Cu/Zn composition63/37 63/37 63/37 63/37 63/37 63/37 properties Plating thickness (μm)0.25 0.25 0.25 0.25 0.25 0.25 Surface layer region (*1) 30 30 31 31 3131 Cu content (*2) Second parameter of copper −0.2 −0.016 −0.25 −0.3−0.5 −0.78 concentration distribution at a depth region of 6 mm Pcontent in plated layer (*3) 1.98 1.70 1.80 2.01 1.80 1.50 (mg/m²)Surface layer region (*1) 2.50 1.50 1.00 1.10 1.00 0.90 P content(atomic %) Rubber Compounding No. B B B B B B composition Amount ofcobalt salt (*4) 2 parts by 2 parts by 2 parts by 2 parts by 2 parts by2 parts by used weight weight weight weight weight weight

[0106] TABLE 3-3 Comparative Comparative Invention Invention InventionInvention Example Example Example Example Example Example 3-1 3-2 3-13-2 3-3 3-4 Initial Rubber adhesion 0 90 100 100 100 100 adhesion ratioafter the property curing of 160° C. × 5 minutes (%) Rubber adhesion 20100 100 100 100 100 ratio after the curing of 160° C. × 9 minutes (%)Rubber adhesion 85 100 100 100 100 100 ratio after the curing of 160° C.× 13 minutes (%) Rubber adhesion 100 100 100 100 100 100 ratio after thecuring of 160° C. × 18 minutes (%) Adhesion Rubber adhesion 50 10 100100 100 100 properties ratio after the after the curing of 160° C. ×deterioration 18 minutes and of 75° C. × the deterioration 100% RH of 2days Rubber adhesion 15 0 90 98 100 100 ratio after the curing of 160°C. × 18 minutes and the deterioration of 4 days Rubber adhesion 0 0 5075 95 100 ratio after the curing of 160° C. × 18 minutes and thedeterioration of 6 days

[0107] TABLE 3-4 Comparative Comparative Invention Invention InventionInvention Example Example Example Example Example Example 3-3 3-4 3-53-6 3-7 3-8 Initial Rubber adhesion 0 30 50 50 60 60 adhesion ratioafter the property curing of 160° C. × 5 minutes (%) Rubber adhesion 1050 75 75 85 90 ratio after the curing of 160° C. × 9 minutes (%) Rubberadhesion 40 75 93 93 95 98 ratio after the curing of 160° C. × 13minutes (%) Rubber adhesion 50 95 98 98 98 100 ratio after the curing of160° C. × 18 minutes (%) Adhesion Rubber adhesion 70 50 100 100 100 100properties ratio after the after the curing of 160° C. × deterioration18 minutes and of 75° C. × the deterioration 100% RH of 2 days Rubberadhesion 50 35 99 100 100 100 ratio after the curing of 160° C. × 18minutes and the deterioration of 4 days Rubber adhesion 30 15 95 99 100100 ratio after the curing of 160° C. × 18 minutes and the deteriorationof 6 days

[0108] Industrial Applicability

[0109] According to the invention, the excellent adhesion property tothe coating rubber containing the reduced adhesion promoter orcontaining no adhesion promoter is ensured by controlling the amount ofphosphorus included as an oxide in the surface layer region of the brassplating applied to the wire constituting the steel cord, so that thereduction or omission of the adhesion promoter in the coating rubbermaterial can be realized without sacrificing the performances of thecord-rubber composite.

[0110] Further, it is possible to stably provide the wire having anexcellent adhesion property to rubber by eliminating factors ofdeteriorating the adhesion property to rubber irrespectively of the sameplating composition.

[0111] Moreover, the adhesion properties after the deterioration can beensured in addition to the initial adhesion property by regulating theconcentration distribution of copper in the plating depth direction.

1. A steel wire for the reinforcement of rubber articles formed bysubjecting a peripheral face of a wire to a brass plating, characterizedin that an amount of phosphorus included as an oxide in a surface layerregion from a surface of the brass plating up to a depth of 5 nm in aradial direction of the wire is controlled to not more than 1.5 atomic%.
 2. A steel wire for the reinforcement of rubber articles according toclaim 1, wherein a ratio of copper to a total amount of copper and zincin the surface layer region is 50-80 atomic %.
 3. A steel wire for thereinforcement of rubber articles according to claim 2, wherein a coppercontent in the brass plated layer is uniform in the radial direction ofthe wire.
 4. A steel wire for the reinforcement of rubber articlesaccording to claim 1, wherein when a distribution of a ratio ofatomicity of copper to total atomicity of copper, zinc, carbon andoxygen at a region from the surface of the brass plating up to a depthof 6 nm in the radial direction of the wire is approximated to quadraticfunction, a parameter in a variable term of second degree of thequadratic function is not more than −0.2 (atomic %/(nm)²).
 5. A steelwire for the reinforcement of rubber articles according to any one ofclaims 1 to 4, wherein an average thickness of the brass plated layer is0.13-0.35 μm.
 6. A steel wire for the reinforcement of rubber articlesaccording to any one of claims 1 to 5, wherein a ratio of copper to sumof copper and zinc in the brass plated layer is 60-70% by weight, and aratio of copper to sum of copper and zinc in the surface layer region is15-45 atomic %.
 7. A steel wire for the reinforcement of rubber articlesaccording to any one of claims 1 to 6, wherein a diameter of the wire isnot more than 0.40 mm.
 8. A steel cord for the reinforcement of rubberarticles, characterized by twisting a plurality of wires as claimed inany one of claims 1 to
 7. 9. A tire comprising a carcass toroidallyextending between a pair of bead portions as a skeleton and a beltdisposed outside the carcass in a radial direction, characterized inthat the steel wire as claimed in any one of claims 1 to 7 or the steelcord as claimed in claim 8 is used in either the carcass or the belt orboth.